1890.] MARINE MOLLUSCA OF ST. HELENA. 309 



Marginella (Volvaria) zonata, Kiener. 



The single specimen from St. Helena is small, about the same size 

 as the form described by Krauss (Siidafr. .Moll. p. 126) under the 

 name M. dunJceri, but the labruin at the upper extremity is united 

 with the shell at the suture and not heloiv it. The position of this 

 point of juncture, judging from the series of specimens in the 

 Museum, is variable, and consequently when it is high up at the 

 suture the upper margin of the brownish-yellow band will fall further 

 below than when the end of the labrum is attached further down or 

 below the suture. I am therefore of opinion that M. dunkeri should 

 be regarded as a variety of M. zonata and not as a distinct species, 

 as the distinctive features referred to by Krauss are not constant. 



Weinkauff (Monograph of Marginella, Conch.-Cab. ed. 2, p. 28) 

 quotes this species as M. dunkeri from Ascension Island, his speci- 

 mens being almost as large as typical examples of M. zonata, which 

 appear to be common at the Cape of Good Hope. 



Mitra simplex, Dunker. 

 Hah. Cape of Good Hope. 



Rissoa platia. (Plate XXIV. fig. 13.) 



Testa minuta, ovato-turrita, imperforata, albida ; anfr actus A\, 

 superne concave excavati, in medio subacute angulati, infra 

 angulum contracti, spiraliter lirati ; apex obtusus, involutus ; 

 apertura rotunde ovata, superne acuminata, longit. totius j 

 subtequans ; peristoma continuum, incrassatum, subeffusum, 

 margine columellari inferne subproducta. 

 Longit. Ij millim., diam. |. 



The spiral sculpture is continued upon the apical whorl, which is 

 involuted, thus producing a very blunt top to the shell. The lirse 

 are four to six in number on the lower half of the penultimate 

 whorl, and rather coarser than those above the angle. 



Rissoa atomus. (Plate XXIV. fig. 14.) 



Testa minuta, alba, pellucida, nitida, ovata, imperforata ; an- 

 fractus 4, convexiusculi, Iceves, idtimus magnus ; apertura sub- 

 pgriformis, longit. totius | adcerptans ; peristoma continuum, 

 margine externo leviter patulo et incrassato, columellari obliqao, 

 superne valde calloso. 

 Longit. 1 millim., diam. |. 



This minute species, of which there are three specimens, is 

 certainly full-grown, and has no other sculpture except microscopic 

 lines of growth. 



Rissoa vaga. (Plate XXIV. fig. 15.) 



Testa ininuta, tenuis, subrimata, dilute fuscescens, spiraliter lirata ; 

 anfractus 5, eonvexi, liris filiformibus spiralibus (in anfr. penult. 

 3, ultimo 1 0) ivstructi ; apertura ovato-rotundata, longit. totius 



